Recently, studies of a micro chemical system utilizing micro-space features have been developed in various fields and a highly-efficient micro chemical system is being constructed which combines plural unit operations such as mixing, extracting, phase separation and the like.
In such a micro chemical system, it has been proposed that reaction is also conducted in a micro reaction flow path. When the chemical reaction is performed using the micro reaction flow path, such a micro flow path is formed in a microchip and sample fluids are mixed in the flow path thereby to perform chemical reaction. This microchip is typically a thin board that has a thickness of several millimeters and has the flow path formed in. Advantageously, it is excellent in heat dissipation, temperature control easiness and small use amounts of sample fluid and reaction solvent.
In addition, an attempt has been made to integrate and perform multi-stage reaction operations in the microchip. One of such applications is synthesis of radiopharmaceuticals used in PET (Positron emission tomography), which is usually conducted at multiple stages. When a radioactive precursor is liquid, it is supplied in form of an aqueous solution. However, organic reaction is often anhydrous reaction that hates water and in order to realize organic reaction, the aqueous solution needs to be exchanged into an organic solvent solution. Besides, as medical agents to be applied to human bodies are finally aqueous solutions, the organic solvent solution needs to be exchanged to an aqueous solution again.
These solvent exchanges are generally conducted by removing a solvent by evaporation and then introducing a new solvent desired to be exchanged. However, this evaporation is difficult to be performed inside the microchip. In the related art, evaporation is performed in a standard container and not in the microchip.
An example of synthesis of radiopharmaceuticals using a microchip is shown in the patent documents 1 and 2, in which, however, reaction is only performed in the chip and evaporation is not performed. Integration of all the steps on the chip has not been realized yet.
First experiment of integration of all the steps of synthesis of radiopharmaceuticals into the microchip is disclosed in the non-patent document 1. In this example, evaporation is an operation through a gas permeation membrane. Therefore, evaporation takes much time even with a small amount of liquid, and the evaporation cannot be performed effectively.
Like this example, synthesis of radiopharmaceuticals is batch synthesis, which needs to pool a batch amount in the microchip. However, the space inside the microchip is an area dominated by the surface tension rather than the gravity, and unless the gas permeation membrane is used, it is difficult to disperse and pool the batch amount in the microchip space.
Besides, in the synthesis of radiopharmaceuticals, there is an operation of distilling a target material by the evaporation of the liquid and transferring it to a next reaction. However, these steps have never been performed in the chip.
As an attempt to perform evaporation in a microchip, there is proposed a method disclosed in the patent document 3. In this evaporation method, as illustrated in FIG. 5, a microchip 1 is used having a gas flow path 2 and a liquid flow path 3 worked asymmetrically therein. Gas and liquid are made to flow into the asymmetrical gas flow path 2 and liquid flow path 3 and the liquid is evaporated from a boundary face between the gas and the liquid. However, a stable flow rate for liquid is limited to about 0.1 μL/min and problematically, concentration of the liquid takes much time. Besides, as the evaporation is performed by making the liquid flow into the liquid flow path 3 and simultaneously concentrating the liquid, it is not suitable for batch synthesis of radiopharmaceuticals or the like.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-520827    [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-527367    [Patent Document 3] International Publication No. WO2003/076038, pamphlet    [Non-Patent Document 1] SCIENCE VOL310 16 Dec. 2005